1. Field of the Invention
The present invention relates to a heat storage material comprising CaCl.sub.2 hydrate for heat storage and radiation with a latent heat in a phase change of fusion and solidification. The heat storage material is used for an air-conditioning, a waste heat recovery or a solar heat storage.
2. Description of the Prior Art
It is most important for the latent heat storage material to be always stable in the repeating heat storage and radiation.
CaCl.sub.2.6H.sub.2 O has been considered to be one of promising heat storage materials, since it has phase change temperature of 29.degree. C. and has a latent heat of 41 cal/g. and is economical. However, when CaCl.sub.2.6H.sub.2 O is repeatedly phase-changed, a crystallization of CaCl.sub.2.4H.sub.2 O (.alpha.-phase: melting point of 45.degree. C.; .gamma.-phase: melting point of 38.degree. C.) is easily caused. When such crystallization is caused, the crystal precipitates at the bottom of the fused liquid. The crystals of CaCl.sub.2.4H.sub.2 O are grown in the repeated phase changes to decrease CaCl.sub.2.6H.sub.2 O as the main component of the heat storage material. Thus, the heat storage capacity of the material is diminished gradually. Such disadvantages can be overcome by the prior invention disclosed in Japanese patent application No. 115450/1980. That is, the crystallization of CaCl.sub.2.4H.sub.2 O is not observed in a heat cycle test (at 35.degree. to 18.degree. C.) for 1,000 cycles when the water content of the heat storage material is controlled in a range of 6.0 to 6.14 moles per mole of CaCl.sub.2.
The crystallization of CaCl.sub.2.4H.sub.2 O can be also prevented by adding a suitable amount of MgCl.sub.2.6H.sub.2 O, MgBr.sub.2.6H.sub.2 O or CaBr.sub.2.6H.sub.2 O according to the other prior inventions disclosed in Japanese Unexamined Patent Publication Nos. 43387/1976, 76183/1976 and 128052/1976. However, it is necessary to use a nucleating agent in the compositions in order to prevent the supercooling. That is, the phase change stability of the heat storage material is depending upon the effect of the nucleating agent. There are various remaining problems such as the kinds of the nucleating agent and the incorporation thereof.